Replacement devices such as artificial joints in general and especially those for the hip have been known for many years. Such replacement devices include substitute members for the two parts of the natural joint, namely the femoral head, which is joined to the femur, and the hip socket, which receives and cooperates with the head to provide a natural universal joint.
Replacement of the natural hip joint parts is necessary when deterioration has occurred to one or both of the natural femoral head and socket. Ideally, the replacement members should reproduce the structure and function of the original members. For example, it is important that the femoral head be securely attached to the femur, that the head be received within the socket and that the resulting joint be produced with the desirable degree of resilience or cushioning.
All known prior art, for example U.S. Pat. No. 4,770,661 and U.S. Pat. No. 4,159,544 disclose a system associated with resorption of bone tissue, protrusion of the bottom of acetabulum, and loosening of the stem due to a relatively high pressure upon the bone. Furthermore, localized pressure generated by the prosthesis parts causes greater than naturally occurring displacement of the stem from its initial position. Particularly, in the upper part, the stem tends to move medially, while in the lower part, it moves outwardly laterally.
Currently used endoprosthesis models typically take into consideration the biomechanics of the femur, which is rather similar to a console. This view is applied both to normal hip joints and total joint replacements and is usually realized by a system configured to rigidly fix the stem of endoprosthesis to the surrounding bone. Typically, to further this goal, the stem may have various geometrical forms for compressive fixation; alternatively or in addition to the specifically designed forms, it is not uncommon to cement the stem to the bone.
The clinical practice and numerous data show that this approach may not fully take into consideration the following:                even after milling of the channel through the femur diaphysis, the femur bone still contains a live tissue requiring circulation of tissue fluid, which may be detrimentally affected by cementing, and        during walking, the femur bone rotates around its long axis thus gradually weakening a bond between this bone and the prosthesis. (See Guide to prosthetics, N. Kondrashin, Moscow, “Medicine” 1988, pages 87,88).        